In the future mobile communication system, transmission of high-speed downlink package data, i.e. data with Internet type, is an important service; the mobile communication system transmits this kind subscriber data based on the subscriber requirement.
The present implementation method of this transmission may be described by taking a method in General Packet Radio Service (GPRS) of a Globe System for Mobile communication (GSM). The method works as follows: all accessed subscribers are in the ready state, i.e. connect to a network; the radio base station uses one carrier, and with one or multiple time slots of this carrier, the downlink data are sent to the subscriber terminal one by one in an omni-directional emission mode that covers one cell or one sector of the base station in order to guarantee that no matter whether the subscriber terminal moves to any position within the covered area, the downlink data can be received. In this case, a base station does not need to know a subscriber terminal position, but only the cell where the subscriber is.
In order to guarantee transmission quality of the downlink data, the ARQ (Automatic Request for Repetition) technique is used in general; that is as follows: while making transmission of downlink data every time, the base station transmits a package having a specific length to the subscriber terminal; having received the package, the subscriber terminal detects whether the received package has error codes using error correction and/or error detection technique (such as redundant correcting technique); when the received package has error codes and cannot be corrected, the subscriber terminal will ask the base station to transmit the package repeatedly.
FIG. 1 shows a typical flow that a base station transmits downlink package data to a subscriber terminal. The mobile communication system knows that: the subscriber terminals 11, 12, . . . 1N are all located at the cell of the base station B, and they are all in a ready state (such as the READY state in GPRS); according to the system signaling, the base station B transmits downlink package data to the terminals 11, 12, . . . 1N sequentially. The head of each package has a subscriber terminal identification, and the package length is determined by the system (usually it is a fixed length that is length of multiple radio frames).
As shown in FIG. 1, the base station B transmits a high-speed downlink package data to subscriber terminal 13 in an omni-directional mode; having received a package, subscriber terminal 13 returns an acknowledgement or an ARQ; then the base station B and subscriber terminal 13 enter the same transmission and acknowledgement procedure of the packages until transmission of the downlink package data from the base station B to subscriber terminal 13 of this time is finished. Then sequentially, the base station B transmits high-speed downlink package data to second subscriber terminal 11; having received an ARQ from the subscriber terminal 11, the base station B transmits the package again in an omni-directional mode; then the base station B and subscriber terminal 11 enter the repeated transmission and acknowledgement procedure of packages until transmission of the downlink package data from the base station B to subscriber terminal 11 of this time is finished.
In another development, the modern mobile communication system applies smart antenna technique, which greatly improves system capacity and performance and reduces system cost.
The basic principle of smart antenna is that: with a received uplink signal from a subscriber terminal, a base station determines the direction of arrival (DOA) of the subscriber terminal, and, beamforming the uplink signal based on the DOA, the base station make directional emission of downlink data to the subscriber terminal.
Obviously, since a base station does not know DOA of a subscriber terminal and if it applies the continuous mode to transmit downlink package data for every subscriber terminal, as mentioned above, only an omni-directional beam can be used; in this case, the advantage of downlink beamforming of smart antenna has not been taken.
Nevertheless, a subscriber terminal is usually moving; for taking advantages of smart antenna, a system must know the current position of every accessed subscriber terminal to guarantee that downlink beamforming is tracking a moving subscriber terminal correctly.
Up till now, there is no solution for the above problems.